The present invention relates to multi-function air data sensing probes (multi-function probes or MFPs) and to total air temperature (TAT) sensors or probes. More particularly, the present invention relates to correction of TAT recovery errors.
Modern jet power aircraft require very accurate measurements of outside air temperature (OAT) for inputs to the air data computer and other airborne systems. The outside air temperature is depended upon, among other things, the total air temperature (TAT) or (Tt). The TAT is the maximum air temperature which can be attained by 100% conversion of the kinetic energy of the flight. The TAT is measured using a TAT sensor or probe, which may or may not be integrated with a multi-function probe (MFP). TAT probes are taught, for example, in U.S. Pat. Nos. 5,653,538 and 5,731,507 which are herein incorporated by reference.
For TAT probes with de-icing heaters, application of the de-icing heat can cause the measured temperature (Tm) to increase at low air speeds. Basically, this effect is a conduction error, internal to the sensor, caused by the close proximity of heated portions of the sensor housing to the sensing element. This is known as de-icing heater error (DHE).
The recovery temperature Tr is the adiabatic value of local air temperature on each portion of the aircraft surface due to incomplete recovery of the kinetic energy. Static air temperature (SAT or Ts) is the temperature of the undisturbed air through which the aircraft is about to fly. One parameter which relates the recovery temperature Tr to the TAT and SAT is called the recovery factor r, which is defined as shown in Equation 1:                     r        =                                            T              r                        -                          T              S                                                          T              t                        -                          T              S                                                          EQ        .                  xe2x80x83                ⁢        1            
The recovery factor is the proportion of kinetic energy converted to heat. A recovery factor of unity means all kinetic energy is converted to heat. In such cases, the recovery temperature Tr is equal to the total temperature. The recovery error is the per unit or fractional total temperature error.
When large local flow angles approach TAT probes, both recovery error and DHE can be large enough to move outside of acceptable limits. The local flow angles are a function or probe placement on the aircraft and flight envelope conditions. Recovery error and DHE are particularly large at low speeds. This also happens to be where the aircraft has the most extreme values of angle of attack (AOA) and angle of sideslip (AOS). The extreme aircraft angles are what cause the extreme local AOAs. A method of accurately measuring the TAT at larger angles of attack would be a significant improvement in the art.
Multi-function probes or MFPs are used in air data systems to provide, among other things, accurate compensation of sideslip of an air vehicle. These MFPs are independent probes that are not pneumatically coupled, but which have processors for interchanging electrical signals between the probes. One type of MFP is the SmartProbe(trademark) sold by the Goodrich Corporation. Multi-function probes include processing circuitry located at the probe itself as part of its instrument package. MFPs can be used, for example, to calculate an MFP local AOA, an aircraft AOA, and an aircraft AOS in addition to airspeed, altitude and Mach number.
A method of generating, for an aircraft, a total air temperature compensated for recovery or deicing heater error includes measuring a total air temperature with a total air temperature probe. A local angle of attack for the total air temperature probe is determined. Then, a corrected total air temperature, compensated for recovery or deicing heater error, is generated as a function of the measured total air temperature and the determined local angle of attack for the total air temperature probe.